1. Field of the Invention
The present invention describes a method to enhance radiation delivery through a barrier that may be encountered during therapeutic laser procedures, particularly where the objective of treatment is to obtain uniform sub-barrier heating and to effect thermal damage to subsurface tissue constituents without destroying or altering the overlying barrier.
2. Information Disclosure Statement
Since its invention in 1960, the laser has found niches in both diagnostic and therapeutic medical applications. Lasers have become widely accepted for treating vascular lesions, comprising enlarged or ectatic blood vessels, pigmented lesions, and tattoos. More recent additions to the list of aesthetic laser treatments include abatement of wrinkles, scars and other blemishes, removal of unwanted hair, creation of skin pockets during hair transplantation surgery and shrinkage of varicose veins. In the above-stated procedures it is necessary to use a sufficient dose of light to irradiate subsurface tissue constituents to achieve the desired clinical effects. However, the delivery of radiation to the appropriate treatment site can be problematic because excessive absorption at the stratum corneum often results in epidermal damage and scattering in the dermal region often results in inadequate heat generation at the treatment site.
Various solutions have been proposed to eliminate the above-stated complications. Generally, the solutions concentrate on increasing the absorption at the treatment site or facilitating transmission through the epidermis.
For example, U.S. Pat. No. 5,226,907 describes a device and method for light-induced hair removal that involves placing an absorptive substance at the treatment site and exposing that substance to the proper wavelength of light. The light-absorbing substance is allowed to migrate at least part-way into the follicle or treatment site. The excess light-absorbing substance is then removed and the area is irradiated to destroy, modify or stimulate the treatment site. However, it is difficult to get the light-absorbing substance or chromophore deep enough into the treatment site to effect destruction, modification, or stimulation of subsurface tissue constituents. Further, this technique results in substantial energy being applied to and absorbed by the epidermis and other skin layers in the region being treated, with significantly reduced energy reaching the treatment area. Therefore, it is difficult to achieve and sustain the critical core temperature that is necessary to destroy, modify or stimulate without damaging the surrounding tissue and without causing pain and injury to the patient.
Whereas, U.S. Pat. No. 5,454,807 describes a device that can facilitate transmission of light through the epidermis. Specifically, a conduit is constructed to deliver a flow of coolant to the surface of a treatment site. Generally cryogen has been used as a coolant to protect the epidermis because the liquid-vapor phase transition of cryogen has been shown to provide a mechanism for selectively cooling the skin. Specifically, the liquid-phase transition of cryogen creates a boundary layer which creates a heat sink below the surface of the skin that can rapidly remove trapped heat before, during, and after laser exposure to protect the epidermis from thermal damage. However, this technique can be counterproductive if a heating effect is desired in the epidermal or upper dermal region because the treatment site will also be cooled and as a result may remain resistant to photothermolysis.
U.S. Pat. No. 5,749,868 describes another method to facilitate transmission of light through the epidermis by using light in the near infrared region to effect a decrease in the ratio of melanin to hemoglobin absorption in the treatment of blood vessels. The method described is, however, limited. First, the method does not provide a way to get through the epidermis. What the invention provides is merely a way to decrease the negative skin-surface side effects (such as hyper-pigmentation) resulting from the treatment. It is evident from the patent description that melanin absorption still occurs at the described treatment wavelengths therefore, some amount of surface damage will still be present, only minimized. The described invention combines the commonly accepted idea that increased penetration can be obtained by using longer wavelengths of light with the use of light in the specific near-IR wavelengths that increase hemoglobin absorption. Second, the invention described addresses exclusively the ratio of melanin to hemoglobin absorption and is therefore limited to blood vessel treatment and is limited in its application.
U.S. Pat. No. 5,000,752 describes a method for transdermal laser delivery through the insertion of an array of surgical needles into a treatment tissue, preventing damage to the skin surface. The needles are attached in a fixed pattern on a flexible pad that allows the entire array to be inserted at one time. However, there are a couple of drawbacks to this invention. First, treatment with the device is painful for the patient. The stratum corneum, or the outermost 10-15xcexc of skin, has no nerve endings. Penetration below that layer, however, causes pain. The device is described as having delivery needles greater in length than the depth of the stratum corneium. Second, the needles employed in the invention are intrusive and increase the chance of infection. The larger the bore of the delivery needle, the larger the entry hole and the greater the chance that microorganisms might be introduced into the site. Third, the invention describes an array of very detailed delivery needles with adjustable, specialized tips. The device must therefore be expensive to manufacture and purchase. Practical application of the invention can be hindered by its cost.
In another example, U.S. Pat. No. 5,735,844 describes a method of improving laser delivery by inserting a needle-like element into the follicle to facilitate light energy reaching the appropriate treatment site. However, this procedure is very painful. On the other hand, if the irradiation source is not inserted into the follicle, it is difficult to get sufficient energy to achieve and sustain the critical core temperature that is necessary to destroy, modify or stimulate without also causing significant damage to the surrounding tissue and thus causing pain and injury to the patient.
An ideal device would enable the irradiation source to be inserted into the treatment site without pain to the patient to improve heat generation at the treatment site and to facilitate the transmission of light energy through the epidermis. Thus, a device and method are needed that will improve transdermal laser delivery without the complications associated with the prior art.
It is an object of the present invention to provide a system and method for improved transbarrier laser delivery to the appropriate treatment site without the complications associated with the prior art.
It is another aim of the present invention to insert the irradiation source, transbarrierly, into the treatment site without pain to the patient to facilitate radiation delivery through the epidermis.
It is a further aim of the present invention to employ pre-treatment methods to further enhance heat generation at the treatment site.
Briefly stated, the present invention describes a system and method to improve radiation delivery through a barrier that may be encountered during therapeutic laser procedures, particularly where the objective of treatment is to produce thermal damage or alterations to subsurface tissue constituents without destroying or altering the overlying barrier. To achieve this result, a bio-compatible fluid is preoperatively administered to the tissue. The bio-compatible fluid is a light-scattering fluid that will scatter light primarily at the desired site thereby achieving a more uniform, enhanced heating over a relatively large treatment area. In addition, a second fluid, a dispersion fluid, can be added to the tissue to function in distributing the light scattering fluid throughout the treatment site. Laser radiation is then administered, through micro pores created for example by a device such as a micro-needle patch, into the treatment site. When a micro-needle patch is employed to deliver the fluid and the radiation, it can be a single patch for both functions, or a separate patch for each function.